Machine for rifling guns



Patented May 18, 1943 MACHINE Fon. ammo GUNS Vannevar Bush, Washington, D. C., assignor to the Government of the United States of America, as represented by the Secretary of War Application January 23, 1942, Serial 1N 427,928]

' 9 Claims. (Cl.'9028.1)

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) The'invention described herein may be manufactored and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to the machining of the barrels of guns and in more detail to the rlfiing of guns having bores of plain or varying form.

In the preferred preeue'e er the method the gun barrel may be constructed in the usual manner and roughly bored to cylindrical form. By

It has been found in practice that guns having tapered bores of various forms have certain notable advantages.

portion, an intermediate tapered or conical portion, and a cylindrical muzzle portion withcurved transition zone between the tapered portion and each of the cylindrical portions. In a barrel of this type'the projectile will be started in a smooth and regular manner, contracted in the tapering portion, and having a section giving it true cylindrical control before it emerges from the muzzle will be more precise in flight than it would be on direct emergence from the conical A desirable form. of such a gun has a bore comprising a cylindrical breech the use of a series of reamers'the bore may 'then be given the desired shape, either conical or composite and having cylindrical end portions and an intermediate conical portion. By following this or any other desired procedure the shape of the bore may be brought to that which is desired for the surface of the lands of the riding.

A rifiing machine preferably constructed as described below is used in forming the riiling grooves inthe bore," In the drawing dimensions are distorted for clarity of explanation, lengths being generally foreshortened. Referring to the drawing by characters of reference Figures 2 to 4 show a guide plug l slightly longer than the barrel to be machined and having a shape complementary to the bore so that it may fill the bore almost completely. In this plug guide a longitudinal guide channel 2 having a straight inner portion. The difllculty of machining such bores has previously rendered their manufacture practical and unduly expensive.

It is therefore a primary object of this invention to present a machine for machining the bores of suchguns which is sufliciently rapid and precise in operation to be practical from a production standpoint.

It is a further object of my invention to produce a machine for riding gun bores which is applicable to guns having straight bores, bores of uniform tape'r, or bores made up of a combination of tapered and cylindrical sections. While the specific description will in general be confined to the latter and more complicated form the modifications required to adapt the device to the simpler forms should be obvious.

The exact nature of the'invention as well as other objects and advantages thereof will clear- Ly appear from the description of the preferred embodiment. as illustrated in the accompanying drawing in which Figure 1 is' a diagrammatic side elevation partially in section. showing a rifling machine constructed according to my invention.

'Figure 2 is a side elevational view partially in section of the plug guide for the rifling machine.

Figure 3 is a side elevational view of the guide taken at right angles to Fig. 2. t

Figure 4 is an end elevational view of the larger end of the guide.

Figure 5 is a fragmentary view similar to Fig. 3

showing a modified form.

Figure 6 is a side elevational view of the chain broaching tool. t

Figure? is'a'top plan view of the chain broaching tool.

wall 3 and side walls disposed at a right angle with respect thereto is milled'out andground to finish the surfaces. Operating in this channel are a pair 01' wedge members 4 and 5. The wedge member 4 has both faces straight and one of thesefaces is in contact with the inner wall 3 of the guide channel. The end 8 of this wedge member 4 protrudes from the large end of the guide for a purpose as will hereinafter appear. The wedge member 5 has a straight inner surface in contact with the outer surface of the wedge member 4 and the outer face 6 of. the wedge member 5 is so formed that it almost corresponds with the shape of the bore; the reason for the, slight difference in conformation being hereinafter explained. End plates 1 secured to the guide I and bridging a part of the channel 2 retain thewedge member 5 against longitudinal movement in the channel but place no restraint upon radial movement thereof. As shown in Fig. 5 the outer wedge 5 may be sup ported against longitudinal movement by means-" of ribs So on the side Walls thereof adapted to slide in grooves 2a in the side walls of the channel 2. When both of these wedge members are in place there remains outside of them an open channel of substantially uniform depth, the

depth of the channel remaining being variable I by longitudinal adjustment member 4.

It should be understood that in practice my invention is not necessarily limited to the use of a plug guide having a shape complemental to the barrel and providing bearing surface for the full length of the barrel. Bearing means need only be provided at the ends of the barrel and of the lower wedge may be of any convenient form capable of supporting in the barrel a guide member having therein a guide channel 2 of the specified form.

" The chain broach comprises a. plurality of links 8, smooth on their sides and of .a width such as to fit in the channel with a smooth sliding engagement.

At spaced intervals in the chain links l3 will be inserted, the links i3 being each equipped with a cutting edge l4 similar in shape ,to that commonly used on breaching tools. The

bottom face of each of the links is formed with rounded projecting ends l adapted to ride on the outer face of the wedge 5. The side faces of each of the links 8 and iii are recessed as best shown in Fig. 6 and connecting bars H are received therein and connected to the links by coupling pins i2 forming a continuous chain slidable through the channel.

At this point it is convenient to describe in detail the shape of the outer face 6 of the outer wedge 5. In determination of this shape it will be convenient to consider that the plug guide i has been tightly inserted in the smooth bore of the unrifled gun. In this condition if a link l3 having a cutting edge 14 is inserted in the guide channel l2 on the outer face of the wedge 5 and the inner wedge 4 moved inward until the cutting edge l4 just touches the inner surface of the gun bore the shape of the outer face 6 should be such that the link l3 may be moved the full length of the channel 2 and the edge l4 will contact the wall of the gun bore at all points along the path. If the gun bore were cylindrical, or tapered uniformly throughout it is apparent that this path would be a straight line parallel to the surface of the bore. When, however, there are cylindrical and conical sections having transition curves in the bore to be machined the shape of the outer face Bwill not quite duplicate that of the longitudinal section of the bore on account of the finite size of the link. The shape is, however, readily determined and milled by a procedure similar to that used in-making cams. In order that the chain may enter the channel without binding, the side walls of the channel external to the section of the guide embraced by the barrel may be slightly relieved.

A preferred form of the assembled rifling machine, with details omitted, is shown in Fig. 1. The plug guide is preferably mounted vertically, large end down on a rigid base I! and the upper end may be steadied by means of an arm and detachable clamp, not shown. The complete chain broach, in endless form, is mounted on a pair of sprockets l8 driven by suitable gearing i1 and so lined up that the chain may be fed directly through the guide channel 2. Around the lower part of the plug guide and coaxial therewith is a rotating collar i8 arranged to be driven by a worm is and ring gear 20 in synchronism with and at a predetermined speed in relation to the gearing driving the breachin chain. The pitch of the rifiing is dependent upon this speed relation This rotating collar is supported on bearings 2| capable of supporting end as well as radial loads and is provided with a socket 22 adapted to embrace the end of the barrel. Set screws 23 or other equivalent means may be provided to insure that the .barrel rotates with the collar. The inner wedge 4 has its large end projecting downwardly below the rigid base 15 and is notched at 24 and so arranged that it can be given astep-like intermittent feeding motion by a lever and pawl 25 or by other known intermittent feed mechanisms. In order to commence the rifling operation the broaching chain may be opened at a readily detachable link and the barrel slipped over the plug guide, breech end down and resting on the rotating collar [4 to which it is clamped to positively receive rotation therefrom. The collar should be so disposed in relation to thebarrel and guide that it will support the barrel in a position in which the bore of the barrel will fit over the guide with allowance for a film of lubricant therebetween. The inner wedge being in its extreme retracted position the'cutting edges l4 will not contact the surface of the bore and the broaching chain may be restoredto endless form on the sprockets. Depending upon the pitch of the riding gearing of the desired ratio will be provided between the worm gear l9 and driving gear I! for the sprockets l6.

at intervals after starting the machine the ratchet mechanism 26 operates, advancing the lower wedge and feeding the cutting edges nearer the surface of the bore. When the wedge has been sufilciently advanced the leading cutting edge will cut a' narrow groove on the inside of the bore, the groove being in helical form as the barrel is being rotated while the cutter advances vertically. Due to the rotation of the barrelthe cutting edge that follows will cut, not in this same groove, but will take the beginning cut for the next adjacent groove of riding. Succeeding cutting edges commence each succeeding groove until a cutting edge has traversed each of the grooves. Following the last of such cutting edges is a section of the chain of slightly greater length than the length or the bore in which there are no cutters. When the last cutting edge has left the bore the feeding device operates to advance the inner wedge and the procedure is then repeated, the cutting edges now deeping and widening each groove in turn. The process of alternate cutting and advancing the cutters continues until the job is finished. It should be noted that several edges are thus cutting simultaneously and that the number of cutting edges should be equal to the number of grooves or some exact multiple thereof. The cutting edges may be mounted at an angle on the links so that the resultant direction of the cutting motion is nearly perpendicular to the cutting edge. It is preferable to cut a narrow groove first and then to widen it to final shape as it is deepened. Obviously, the form given the cutting edge will determine the shape of the groove.

Normally the speed of .the cutting chain should be about 30 feet per minute, and at the beginning of the run the feed ratchet should be so adjusted that the depth of cuts will be about .004". These values will, of course, be dependent upon the 1 physical characteristics of the material employed in the gun barrel but in the ordinary case the Job or rifling a gun of small size should not take more than ten minutes after the set-up is completed.

Since the angle between the cutting edge and the groovebeing cut varies slightly as the edge is moved through the bore, the cutting tool should be given such rake and clearance all around its active portion that proper cutting action willbe obtained in spite of the change in angle. Due to this same change of angle the groove will not be of quite the same cross sectional shape throughout but as the barrel engaging portion of the shell is being compressed radially as it progresses through the bore the variation in groove section will not allow gas leakage therethrough.

If it is desired to vary the depth of the groove along the bore, this can be accomplished by varying the shape of the outer face 6 of the outer wedge from that previously detailed, which resuits in a groove of uniform depth.

It is also possible to control the width of grooves of regular dimensions, say a groove of generally right angular form having rounded corners. To

do this the grooves may first be cut as described above, then the gear ratio'changed to slightly,

alter the pitch, and the grooving repeated, being sure of initial registry. This will alter the width of the groove as it passes along the bore.

Various other refinements are possible, but for the usual case it is believed that grooves of uni* form or slightly decreasing depth are'preferable, and that a slight narrowing of the width of the groove, in proceeding from the 'breech of the muzzle, is desirable.

In guns of conical bore there is a deformation g of the barrel engaging portion or the shell as the shell progresses through the gun. and this may reach extreme limits. This radial compression will occur at both the grooves and the lands, I

accompanied by longitudinal extension of the barrelengaging portion of the shell. Whether the depth of the grooves should be uniform,

I claim: V

1. Apparatus for riding the bore of a. gun comprising spaced cutters connected in chain rashion, means to guide said cutters in a path substantially parallel to the longitudinal profile oi the surfac or said bore, said path being constrained by said guiding means to a plane includingthe axis of the bore, means to advance said cutters along said path, and means to rotate I said barrel about its axis as said cutters are advanced whereby said cutters trace helical path in the wall of said bore.

2. Apparatus for rifiing the bore of a gun barrel comprising a body of a length at least as great as that of the barrel and adapted to be inserted therein, a longitudinal guide channel'in said body,

' a plurality of spacedlcutrters connected in chain fashion and slidable in said guide channel, aajustable means to place said cutters in cutting relation with the wall of said borewhen said body 11s inserted in the'barrel, means to advance said cutters longitudinally in said channel, and means operating in geared relation to said last 'mentioned means adapted to rotate the barrel about its axis as said cutters are advanced longitudie nally thereof.

3. Apparatus for rifling the bore ofa gun bar- "rel comprising a body of a length at least as great as that of thebarrei and adapted to be inserted in said bore, means on said body adapted to support said barrel for rotation about the axis of the barrel while'the barrel is surrounding said body, a longitudinal guide channel in said body, a plurality of spaced cutters connected in chain fashion and slidable in said guide channel. adjustable radial guide means in said channel inside of said cutters, means to advance'said cutters longitudinally in said channel, and means operating simultaneously and in relation to said last mentioned means adapted to rotate said barrel about its axis as said cutters are advanced longitudinally of said axis whereby said cutters trace helical paths in the wall of said bore. j

4. The apparatus described in claim 3, the

means on said body adapted to support said bar-.

relcomprising portions of said body of a size and shape adapted to engage the wall of said bore.

5. The apparatus described in claim 3, said radial guide means comprising a pair of wedge members in said'channel, one of said wedge members being longitudinally adjustable and the other of said wedge members being longitudinally fixed but radially free whereby longitudinal adjustment of said adj ustable wedge member may vary the depth of the said guide channel'outside oi! said wedge members.

' dial guide means comprising a, guide member ex-.

6. The apparatus described in claim 3, said rate'nding at'least the full length of said channel, anda track surfaceon said guide member upon which said spaced cutters are sl dable, the longitudinal profile of said track surface being such that the path followed by the cutting edges of said cutters as they are movedlongitudinally thereof will be substantially parallel to the longitudinal profile or the urface of the bore in which said body is inserted.

7. Apparatus for rifiing the bore of a gun barrel comprising a body having a length at least as great as the barrel and adapted to be inserted in the bore or a gun barrel, a collar surrounding and rotatably mounted on an end of said body. adapted to eng ge a gun barrel to rotate the same about said body, a longitudinal guidechannel in said body,sprockets rotatably mounted on the ends of said bodyin tangential alignment with said guide channel, means to regulate the depth of said guide channel, an endless chain of links slidable through said channel and engaged on I said sprockets, a plurality of cutters on spaced links of said chain, means to rotate said sprockets to draw said cutters through said guide channel,

- and means operating simultaneously and in geared relation to said last mentioned means to rotate said. collar'whereby said cutters may be caused to trace helical paths on the walls or s'ai bore.

a. The apparatus described in claim ,7, said body comprising a plug-like member having a size and shape complementary to the shape of the bore in the barrel to be rifled.

exact multiple of the number of grooves to be I formed in the bore, a section of said chain of length at least as great'as said barrel following said cutter carrying links, the links of said section being without cutters, and intermittent feed meansadapted to decrease the depth of said guide channel during each interval that said section is engaged in said channel. i

. VANNEVAR BUSH. i 

